It's not only carnivorous plants that bugs have to watch out for. Sure, if an ant tumbles into a pitcher plant or a spider stands in the open maw of a Venus flytrap, we know what's coming next. But certain innocent-looking plants—perhaps very many of them, even including ones in your own yard—murder hosts of insects that they have no plans to eat. They lure passing bugs into a slow death, then exchange their corpses with other insects for...